Variable resistors and potentiometers



NOV. 4, 1958 J, QUlNT 2,859,314

VARIABLE RESISTORS AND POTENTIOMETERS Filed Oct. 29, 1956 2 Sheets-Sheet1 Nov. 4, 1958 B. H. J. QUINT 2,859,314

VARIABLE RESISTORS AND POTENTIOMETERS Filed Oct. 29, 1956 2 Sheets-Sheet2 mus/V702 5. m emf United States Patent VARIABLE RESISTORS ANDPOTENTIOMETERS Bernard Henry John Quint, Swindon, England, assignor toThe Plessey Company Limited, Ilford, England, a British companyApplication October 29, 1956, Serial No. 619,076

Claims priority, application Great Britain November 4, 1955 8 Claims.(Cl. 201-55) This invention relates to variable resistors andpotentiometers, hereinafter jointly referred to as variable resistordevices, of the kind in which a contact or wiper arm has two contactpoints adapted to wipe respectively along two tracks arrangedconcentrically about a spindle on which the arm is mounted. In awell-known construction of such resistor or potentiometer the armcomprises three parts. A stop or driving plate is secured on the spindleand is provided with an abutment co-operating with fixed stop means forlimiting the rotation of the shaft, and in many cases a further abutmentmeans for actuation of an on-and-off switch; an insulating plate issecured to the stop plate; and the arm is completed by a spring attachedto the insulating plate. In many cases this spring is shaped withsuitable contact parts for sliding co-operation with two concentrictracks, of which generally the inner one is a collector ring, whereasthe outer one is the resistance track; in other cases the spring isprovided with a carbon brush at one or both contact points.

The present invention has for an object to provide a simplifiedconstruction of the arm. According to the invention the wiper armcomprises a resilient plate of flexible material mounted on the spindlewith its plane perpendicular to the spindle axis, a floating contactbrush for co-operation with the two tracks, and a bridge member ofinsulating material which connects the brush member to, and transmitspressure thereto from, the resilient plate. Preferably the plate ofspring steel or other resilient material is sub-divided by slots orapertures into a central part which is adapted to be secured on thecontrol shaft and is extended to one side of the shaft to form anabutment for co-operation with fixed stop means to limit the movement ofthe arm, and an outer part which is located at the opposite side of theshaft and is connected with the remainder of the plate by narrow andtherefore more readily flexible strips substantially parallel to thecentre line of the arm. These flexible strips allow the outer part toyield resiliently longitudinally of the shaft. The sliding contactsproper are provided in suitable spatial relation on a floating brush,which is connected to the arm by a bridge member. The latter is securedto the outer part of the plate in such manner as to be resilientlyapplied by the resilient action of the plate on the bridge member to thetwo contact tracks and move around the shaft jointly with the springplate While being pivotally movable relative thereto about an axis whichextends tangentially to such rotary movement. The bridge member or pivotmeans includes an insulating body, by which the contact parts areelectrically insulated from the shaft. An abutment for operating anon-and-oif switch may be formed on the spring plate by bending upwardlya tongue extending longitudinally of the arm, which is blanked out ofthe abutment part of the plate and bent up about its edge adjacent tothe shaft. For greater rigidity the bent-up portion is preferable curvedabout an axis parallel to the shaft, and in order to compensate for theloss of rigidity of the abutment part of the plate due to the blankingout of the tongue, an embossed ridge may be provided on the plate alongthe two lateral edges of the cut-out portion, said ridge being continuedif desired by a further ridge extending along one or both of the otheredges of the cutout portion. The pivot axis about which the bridgemember can moverelative to the spring plate, is preferably arrangednearer to the resistance track than to the collector ring, so that dueto the different leverage, greater contact pressure is applied at thepoint of contact with the former than at the point of contact with thelatter.

The pivotal connection between the bridge member and spring plate ispreferably effected by a yoke plate of insulating material which isprovided at one side with a tongue or tongues engaging a slot, or a lineof slots or notches, provided in the spring plate, and the other end ofwhich is adapted to engage grooves or notches in the brush member so asto pivot jointly with the latter in the said slot or slots or notches ofthe spring plate. The brush member may consist of a substantiallyrectangular block of carbon provided at one surface with two roundedhumps serving as contact points, the block being provided on twoopposite sides with parallel grooves for engagement by the sides of aU-shaped cut-out provided in the yoke member. According to amodification, the brush member may consist of sheet metal bent in U-shape to provide a bottom surface and two side walls extendinglongitudinally of the arm. The contact points are constituted bydimpling out parts of the bottom. The bent-up side walls are provided attheir free edges opposite to the base with notches into which the yokemember is adapted to engage with the bottom edge of its U-shapedcut-out. The spring plate may be secured to the control shaft by beingspun over a reduced diameter extension at one end thereof, and whilehitherto it was generally necessary to use a high-grade material havinghigh corrosion resistance and low electrical resistance, for exampleberyllium copper, nickel silver, or Phosphor bronze, the spring plateaccording to the present invention may be made from ordinary springsteel.

The accompanying drawing illustrates an embodiment of the invention;

Fig. l is a sectional elevation of the variable resistor,

Fig. 2 is an end elevation,

Fig. 3 is an exploded view showing one end of the spring plate with theyoke plate and brush, and

Fig. 4 is a perspective view showing another form of brush.

Referring now to the drawing, the potentiometer has a part-circularresistance track 6 and a contact ring 5 concentrically embedded in aninsulating base 10.

Mounted rotatably in a bush 11 secured to the base is a spindle 4, and ablade 1 of spring steel or other resilient material is secured on thespindle 4 by means of a reduced-diameter end portion 4a of the spindle,which extends through a corresponding hole in the plate 1 and is spunover at its outer end so that the plate 1 will rotate jointly with theshaft.

A carbon brush 3 having two projecting contact humps c is secured to theplate 1 by a bridge or yoke 2 of insulating material in such manner asto be able to pivot about a fulcrum which is tangential to the armmovement about the spindle 4 to distribute the resilient pressure of theplate 1 to the two contact humps c. The two humps c are respectively incontact with the resistance track 6 and the contact ring 5. Thepotentiometer is enclosed in a housing 12, which in a well known mannercarries an on-off switch 13 which is automatically operated by anabutment member g carried by the arm plate 1 when the latter moves toand from one end of its movement. The housing also carries end stopmeans 12a which co-operate with an abutment f an arm 1 for limitingthejrotary movement of the arm about the spindle axis.

Referring now more particularly to the construction of the wiper arm,the spring plate it is provided with a slot a into which a reduced-widthcentre part in at one end of the yoke member 2 engages, while the U-shaped cut-out 2b at the opposite end of the yoke member engages groovesb at the two Sides of the carbon brush 3.

A cut-out e separates the contact-carrying part lb of the spring plate 1from an abutment-carrying part to. The latter is provided with theabutment f. A curved tongue g is cut out of an aperture 5 and bent up asshown to operate the on-and oif switch 13, and a reinforcing ridge h ispressed out around the aperture i. The yoke 2 engages the bridge member3 at a point nearer to the hump c which cooperates with the resistancetrack 6 than to the other hump, so that greater contact pressure isapplied on the resistance track 6 than on the contact ring 5.

Fig. 4 shows a metal brush 3a which may be used in place of the carbonbrush 3 of Fig. 3, and which is formed of bent sheet metal. Notches aare provided for engagement by the yoke 2.

What I claim is:

1. A variable resistor including; a body member; a spindle rotatablymounted on said body member; a resilient plate carried by said spindleand constrained to rotate therewith, the plate extending transversely ofthe spindle; first and second concentric tracks supported by the bodymember, the tracks being concentrically arranged around the axis ofrotation of said spindle; a floating brush member for wipingco-operation with each of the tracks, a member of insulating materialwhich connects the brush member to, and which transmits pressure theretofrom, the resilient plate; a stop member on the resilient plate limitingthe range of rotation of the spindle; and an abutment on the resilientplate for operating an on and olf switch means.

2. A variable resistor including a body member; first and second trackssupported by the body member the tracks being concentric; a rotatablespindle located at the centre of the tracks; a resilient plate carriedby the spindle and constrained to rotate therewith, the plate extendingtransversely of the spindle to overlie at least a part of said body thatis intersected by said tracks, said plate being sub-divided by anaperture to provide a first part which is connected to the spindle, andwhich first part is extended to one side of the spindle to form a stopmeans for limiting the angular range of the rotary movement of the arm,and a second part, which is located at the opposite side of the spindleto the first part, which second part is connected with the remainder ofthe plate by narrow, and therefore more flexible, strips extendingsubstantially parallel to the centre line of the plate; a floating brushmember for wiping co-operation with each of the tracks; a member ofelectrically insulating material connecting the brush member to thesecond part of the plate, in such manner that the resiliency of theplate acts always to maintain the said wiping cooperation; and anabutment on the resilient plate for operating an on and off switchmeans.

3. A variable resistor including; a body member, a spindle rotatablymounted on said body member; a re silient plate carried by said spindleand constrained to rotate therewith, the plate extending transversely ofthe spindle; first and second concentric tracks supported by the bodymember, the tracks being concentrically arranged around the axis ofrotation of said spindle; constact members for wiping co-operation Witheach of the tracks, a member of insulating material which floatinglyconnects the contact member to the resilient plate; and which transmitspressure to the contact member from the resilient plate; a stop memberon the resilient plate limiting the amount of angular rotation of thespindle; and an abutment on the resilient plate for operating an on-offswitch means, the abutment being formed by bending upwardly a tongueextending longitudinally of the resilient plate, which tongue is blankedout of the plate, at a location between the stop member and the spindle,and which is deformed about its edge adjacent to the shaft.

4. A variable resistor including; a body member; first and secondconcentric annular tracks supported by the body member; a rotatablespindle located at the centre of the tracks; a resilient plate carriedby the spindle and constrained to rotate therewith, the plate extendingtransversely of the spindle to overlie at least a part of said body,that is intersected by said tracks, said plate being sub-divided by atleast one aperture, into a first part which is connected to the spindle,and which is extended to one side of the spindle to form stop means forlimiting the angular range of the rotary movement of the arm, and asecond part, which is located at the opposite side of.the spindle to thefirst part which second part is connected with the remainder of theplate by narrow, and therefore more flexible, strips extendingsubstantially parallel to the centre line of the plate; a floating brushcontact member for wiping co-operation with each of the tracks; a memberof electrically insulating material connecting the brush contact memberto the second part of the plate, in such manner that the resiliency ofthe plate acts always to maintain the said wiping cooperation; and anabutment for operating an on and otf switch located, that abutment beinglocated between the stop means and the spindle, and consisting of atongue which has been produced by a blanking operation, and which isintegrally connected with the plate at a location adjacent the spindle.

5. A variable resistor as claimed in claim 4, in which said tongue has acurved cross-section in a plane taken transverse to the axis of rotationof the spindle.

6. A variable resistor as claimed in claim 4, wherein a strengtheningridge is provided in the resilient plate, the ridge being located insaid first part and adjacent two lateral edges of the aperture left bythe blanking out of the tongue.

7. A variable resistor including; a body member; a first track ofresistor material; a second track serving as a collecting trackconcentrically arranged relative to the first track; a rotatable spindlelocated at the centre of the tracks; .a resilient plate carried by thespindle and constrained to rotate therewith, the plate extendingtransversely of the-spindle to overlie at least a part of said body,that is intersected by said tracks, said plate being sub-divided by anaperture to provide a first part which is connected to the spindle, andwhich first part is extended to one side of the spindle to form stopmeans for limiting the angular range of the rotary movement of the armand second part, which is located at the opposite side of the spindle tothe first part which second part is connected with the remainder of theplate by narrow, and therefore more flexible, strips extendingsubstantially parallel to the centre line of the plate; a contact memberfor wiping co-operation with the first and second tracks; a member ofelectrically insulating material floatingly connecting the brush contactmember to the outer part of the plate, the fulcrum axis about which thebrush contact member can pivot relative to the plate being nearer to thefirst track than to the second track whereby, owing to the differentleverage, greater contact pressure is applied by the resilient plate atthe point of contact of the brush contact member with the first trackthan with the second track; and an abutment on the resilient plate foroperating an on and off switch means.

8. A variable resistor as claimed in claim 2, wherein the brush contactmember is shaped as a substantially rectangular block having in twoopposite side walls slots for engagement by the sides of the member ofelectrically insulating material.

References Cited in the file of this patent UNITED STATES PATENTS

